Multi-mode radio with interference cancellation circuit

ABSTRACT

A multi-mode wireless transmit/receive unit (WTRU) includes at least one antenna, first and second communication mode receivers and a first communication mode transmitter. The first and second receivers simultaneously receive signals from the antenna. The first transmitter generates and sends a first type of signal to the antenna while, at the same time, the second receiver receives a second type of signal from the antenna. In a preferred embodiment, the WTRU further includes a vector multiplier configured to reduce or eliminate interference of signals received by the second receiver, the interference being caused by the first transmitter. The vector multiplier adjusts the phase and amplitude of noise (i.e., spurious in-band noise) measured by the second receiver. The WTRU may further include a second communication mode transmitter configured to generate and send a second type of signal to the antenna.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional PatentApplication Ser. No. 60/473,600, filed May 27, 2003, which isincorporated by reference as if fully set forth herein.

FIELD OF THE INVENTION

The present invention relates generally to wireless communicationsystems. More particularly, the present invention relates to attenuatingspurious transmissions which interfere with communications received by areceiver in a wireless communication system.

BACKGROUND

In a conventional cellular communication system including a plurality ofwireless transmit/receive units (WTRUs), (i.e., user equipments (UEs),radios, mobile platforms, handsets), and a network, the WTRUs arerequired to measure signals from different cells in order to find basestations with the strongest signal and report them to the network forfacilitating handover (connected mode) and cell reselection (idle mode).When a new base station with a stronger signal than a current servingbase station is measured, the network will instruct the respective WTRUto handover to the new base station. These measurements are typicallyperformed on common channels, such as the pilot channel in Code DivisionMultiple Access (CDMA) networks and the Broadcast Control Channel (BCCH)in Global System for Mobile communications (GSM) networks.

Multi-mode WTRUs support more than one Radio Access Technology (RAT).For example, a multi-mode WTRU may include support for UniversalTerrestrial Radio—Frequency Division Duplex (UTRA-FDD) CDMA and GSM.Usually, multi-mode WTRUs are required to support handover betweendifferent RATs. Such handovers are referred to as inter-RAT handovers.

A problem arises for the case of multi-mode WTRUs in which one of themodes requires constant transmissions. For example, during an activeUTRA-FDD CDMA call, i.e., when in “connected mode”, the WTRUscontinuously transmit and receive in different frequency bands. In orderto make a measurement for an inter-RAT handover, such as to a GSM orTime Division Synchronous Code Division Multiple Access (TD-SCDMA)network, the WTRU must stop transmitting during the measurement period.Otherwise, emissions from the CDMA transmitter will interfere with thereceiver belonging to the other RAT.

FIG. 1 illustrates the interference problem described above. A frequencyspectrum 100 includes a UTRA-FDD signal in the 1920–1980 MHz band 105having spurious emissions 110 that fall within the GSM Digital CellularSystem (DCS) 1800 receive band 115 from 1805–1880 MHz. The UTRA-FDDsignal 105 itself acts as a large out-of-band blocker for the GSMreceiver and desensitizes the receiver if not attenuated. Knownpractical filter solutions provide some attenuation of the UTRA-FDDsignal, but the small frequency spacing and cost/size constraintsresults in inadequate filtering which does not affect the level of thespurious transmission from the UTRA-FDD transmitter.

Networks that require continuous transmissions using multi-modeoperation avoid this problem by allowing the WTRU to create gaps in itstransmissions. During the gap period, the WTRU stops transmitting to theserving cell. Instead, the WTRU receives signals from neighboring cellsbelonging to a different system. For example, by implementing acompressed mode in UTRA-FDD, the WTRU is able to take advantage of thegaps in transmissions to make measurements on GSM cells.

FIG. 2 illustrates an example of a conventional WTRU 200 whichimplements a compressed mode operation. The WTRU 200 includes an antenna205, a system switch 210, a duplexer 215, a universal mobiletelecommunications system (UMTS) receiver (Rx) 220, a UMTS transmitter(Tx) 225, a transmit/receive switch 230, a bandpass filter 235, a GSM Rx240, and a GSM Tx 245. The system switch 210 is used to selectivelyconnect the antenna 205 to one of a UMTS (e.g., UTRA-FDD) radio or a GSMradio. By implementing the compressed mode, cell capacity is reducedbecause communications which occur between the WTRU 200 and the networkis interrupted during the above-mentioned transmission gaps. Amulti-mode radio that simultaneously receives signals from a UTRA-FDDcell and a Time Division Multiple Access (TDMA) cell to avoid such aninterruption in communications is desired. Furthermore, a multi-moderadio that allows the GSM Rx 240 to receive signals without interferencefrom the UMTS Tx 225 is also desired.

SUMMARY

A multi-mode WTRU includes at least one antenna, a first communicationmode receiver, a second communication mode receiver and a firstcommunication mode transmitter. The antenna is configured to receive andtransmit at least two different types of signals. The firstcommunication mode receiver is configured to receive a first type ofsignal from the antenna. The second communication mode receiver isconfigured to receive a second type of signal from the antenna. Thefirst communication mode transmitter is configured to generate and sendthe first type of signal to the antenna. The first and secondcommunication mode receivers simultaneously receive signals from theantenna. The first transmitter sends the first type of signal to theantenna while, at the same time, the second receiver receives the secondtype of signal from the antenna.

The WTRU may further include a vector multiplier configured to reduce oreliminate interference of signals received by the second communicationmode receiver, the interference being caused by the first communicationmode transmitter. The vector multiplier adjusts the phase and amplitudeof the interference.

The WTRU may further include a second communication mode transmitterconfigured to generate and send the second type of signal to theantenna, and a switch in communication with the antenna. The switch maybe configured to selectively connect the second communication modetransmitter to the antenna, prevent signals from the antenna to reachthe first and second communication mode receivers, and prevent the firstcommunication mode transmitter from sending the first type of signal tothe antenna.

The first communication mode receiver may be a universal mobiletelecommunications system (UMTS) receiver. The second communication modereceiver may be a global system for mobile communications (GSM)receiver. The first type of signal may be a frequency division duplex(FDD) signal. The first type of signal received by the firstcommunication mode receiver may be originated by a universal terrestrialradio access (UTRA)-FDD cell. The second type of signal may be aTDMA-FDD signal. The second type of signal received by the secondcommunication mode receiver may be originated by a universal terrestrialradio access (UTRA)-TDD cell. The second type of signal received by thesecond communication mode receiver may be originated by a global systemfor mobile communications (GSM) cell.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description of a preferred example, given by way of exampleand to be understood in conjunction with the accompanying drawingwherein:

FIG. 1 provides an example of interference in a multi-mode WTRU;

FIG. 2 shows an example of a conventional multi-mode WTRU requiringcompressed mode for performing measurements; and

FIG. 3 provides a system block diagram of a WTRU incorporating aninterference cancellation circuit in accordance with a preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a description of a preferred embodiment of a WTRU orintegrated circuit (IC) used to communicate with a UTRA-FDD cell of awireless multi-cell FDD communication system while receiving signalsfrom a TDMA cell, such as a GSM or UTRA-TDD cell. When the WTRU is notin a connected mode, the WTRU must periodically search for new basestations. Typically the WTRU must do this as efficiently as possible tominimize power consumption, thus maximizing battery life. This can beperformed most efficiently if the WTRU can simultaneously receivesignals from an FDD cell and a TDMA cell.

Preferably, the present invention disclosed herein is incorporated intoa wireless transmit/receive unit (WTRU). Hereafter, a WTRU includes butis not limited to a user equipment, mobile station, fixed or mobilesubscriber unit, pager, or any other type of device capable of operatingin a wireless environment. The features of the present invention may beincorporated into an IC or be configured in a circuit comprising amultitude of interconnecting components.

The present invention is applicable to communication systems using TDD,TDMA, FDD, CDMA, CDMA 2000, time division synchronous CDMA (TDSCDMA),and orthogonal frequency division multiplexing (OFDM). However, thepresent invention is envisaged to be applicable to other types ofcommunication systems as well.

FIG. 3 is a block diagram showing a preferred embodiment of ainterference cancellation system which is incorporated into a WTRU 300.The WTRU includes an antenna 305, a transmit/receive switch 310, atriplexer 315, first coupler 320, second coupler 325, a UMTS Rx 330, aUMTS Tx 335, a GSM Rx 340, a GSM Tx 345, a bandpass filter 350, anin-phase/quadrature (I/Q) vector multiplier 355, a interference cancelercontrol circuit 360 and a modem 365. When the VVTRU 300 is in a receivemode, signal arriving at the antenna 305 are forwarded to thetransmit/receive switch 310. The transmit/receive switch 310 connectsthe antenna to the triplexer 315 for UMTS and GSM Rx operation. When theWTRU 300 is in a GSM Tx mode, the transmit/receive switch 310 connectsthe antenna to the GSM Tx 345 during GSM transmissions.

The triplexer 315 routes three different signals: a UMTS Rx signal 370,a UMTS Tx signal 375 and a GSM Rx signal 380. The UMTS Tx signal 375consists of a UMTS transmission generated by UMTS Tx 335 which includesspurious emissions. While the UMTS Tx signal 375 itself may be isolatedfrom the GSM receiver 340 by the triplexer 315 and another possiblefilter in front of the GSM receiver 340, a portion of the spuriousemissions will fall in the GSM receive bandwidth and will result in aleakage 385, consisting of UMTS Tx spurious in-band noise, onto the GSMRx signal path 380. This leakage 385 must be removed or else the GSM Rx340 will be desensitized.

An interference cancellation configuration consisting of the bandpassfilter 350, I/Q vector multiplier 355, and interference canceler controlcircuit 360, provides the required attenuation of the leakage 385. Theoutput of the UMTS transmitter 335 is sampled by the first coupler 320and passes through the bandpass filter 350 to the I/Q vector multiplier355. The I/Q vector multiplier 355 adjusts the phase and amplitude ofthe sampled UMTS transmit signal in response to Vi (in-phase voltage)and Vq (quadrature voltage) signals provided by the interferencecanceler control circuit 360 to minimize the noise seen by the GSM Rx340. The resulting signal 390 output from the I/Q vector multiplier 355is combined with the GSM Rx signal 380 via the second coupler 325.

The phase and amplitude of the sampled UMTS signal are adjusted usingthe Vi line 392 and the Vq line 394 on the I/Q vector multiplier 355according to the following equations:Amplitude=10 log((Vi^2+Vq^2)/2Vref^2))   Equation 1;andPhase=arc tan(Vq/Vi)   Equation 2.

The interference canceler control circuit 360 receives measurements ofthe noise measured by the GSM receiver 340 via the modem 365, andadjusts the Vi signal 392 and the Vq signal 394 until the phase andamplitude of the I/Q vector multiplier 355 minimizes the noise. The UMTSTx leakage 385 may be attenuated by 30 dB, allowing enhanced receptionof the GSM Rx signal while transmitting on the UMTS bands.

While this invention has been particularly shown and described withreference to preferred embodiments, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the scope of the invention describedhereinabove.

1. A multi-mode wireless transmit/receive unit (WTRU) comprising: (a) atleast one antenna configured to receive and transmit at least twodifferent types of signals; (b) a first communication mode receiverconfigured to receive a first type of signal from the antenna; (c) asecond communication mode receiver configured to receive a second typeof signal from the antenna; (d) a first communication mode transmitterconfigured to generate and send the first type of signal to the antenna,wherein the first and second communication mode receivers simultaneouslyreceive signals from the antenna, and the first transmitter sends thefirst type of signal to the antenna while, at the same time, the secondreceiver receives the second type of signal from the antenna; (e) atriplexer electrically coupled to the first communication mode receiver;(f) a transmit/receive switch electrically coupled to the antenna andthe triplexer; (g) a first coupler electrically coupled to the triplexerand the first communication mode transmitter; (h) a second couplerelectrically coupled to the triplexer and the second communication modereceiver; (i) a bandpass filter electrically coupled to the firstcoupler; and (j) a vector multiplier electrically coupled to thebandpass filter and the second coupler, the vector multiplier configuredto reduce or eliminate interference of signals received by the secondcommunication mode receiver, the interference being caused by the firstcommunication mode transmitter, wherein the vector multiplier adjuststhe phase and amplitude of the interference.
 2. The WTRU of claim 1further comprising: (k) a second communication mode transmitterelectrically coupled to the transmit/receive switch, the secondcommunication mode transmitter configured to generate and send thesecond type of signal to the antenna, wherein the transmit/receiveswitch is configured to selectively connect the second communicationmode transmitter to the antenna, prevent signals from the antenna toreach the first and second communication mode receivers, and prevent thefirst communication mode transmitter from sending the first type ofsignal to the antenna.
 3. The WTRU of claim 1 wherein the firstcommunication mode receiver is a universal mobile telecommunicationssystem (UMTS) receiver.
 4. The WTRU of claim 1 wherein the secondcommunication mode receiver is a global system for mobile communications(GSM) receiver.
 5. The WTRU of claim 1 wherein the first type of signalis a frequency division duplex (FDD) signal.
 6. The WTRU of claim 5wherein the first type of signal received by the first communicationmode receiver is originated by a universal terrestrial radio access(UTRA)-FDD cell.
 7. The WTRU of claim 1 wherein the second type ofsignal is a time division multiple access (TDMA) signal.
 8. The WTRU ofclaim 7 wherein the second type of signal received by the secondcommunication mode receiver is originated by a universal terrestrialradio access (UTRA)-TDD cell.
 9. The WTRU of claim 7 wherein the secondtype of signal received by the second communication mode receiver isoriginated by a global system for mobile communications (GSM) cell. 10.An integrated circuit (IC) used in combination with at least one antennaconfigured to receive and transmit at least two different types ofsignals, the IC comprising: (a) a first communication mode receiverconfigured to receive a first type of signal from the antenna; (b) asecond communication mode receiver configured to receive a second typeof signal from the antenna; (c) a first communication mode transmitterconfigured to generate and send the first type of signal to the antenna,wherein the first and second communication mode receivers simultaneouslyreceive signals from the antenna, and the first transmitter sends thefirst type of signal to the antenna while, at the same time, the secondreceiver receives the second type of signal from the antennas; (d) atriplexer electrically coupled to the first communication mode receiver;(e) a transmit/receive switch electrically coupled to the antenna andthe triplexer; (f) a first coupler electrically coupled to the triplexerand the first communication mode transmitter; (g) a second couplerelectrically coupled to the triplexer and the second communication modereceiver; (h) a bandpass filter electrically coupled to the firstcoupler; and (i) a vector multiplier electrically coupled to thebandpass filter and the second coupler, the vector multiplier configuredto reduce or eliminate interference of signals received by the secondcommunication mode receiver, the interference being caused by the firstcommunication mode transmitter, wherein the vector multiplier adjuststhe phase and amplitude of the interference.
 11. The IC of claim 10further comprising: (j) a second communication mode transmitterelectrically coupled to the transmit/receive switch, the secondcommunication mode transmitter configured to generate and send thesecond type of signal to the antenna, wherein the transmit/receiveswitch is configured to selectively connect the second communicationmode transmitter to the antenna, prevent signals from the antenna toreach the first and second communication mode receivers, and prevent thefirst communication mode transmitter from sending the first type ofsignal to the antenna.
 12. The IC of claim 10 wherein the firstcommunication mode receiver is a universal mobile telecommunicationssystem (UMTS) receiver.
 13. The IC of claim 10 wherein the secondcommunication mode receiver is a global system for mobile communications(GSM) receiver.
 14. The IC of claim 10 wherein the first type of signalis a frequency division duplex (FDD) signal.
 15. The IC of claim 14wherein the first type of signal received by the first communicationmode receiver is originated by a universal terrestrial radio access(UTRA)-FDD cell.
 16. The IC of claim 10 wherein the second type ofsignal is a time division multiple access (TDMA) signal.
 17. The IC ofclaim 16 wherein the second type of signal received by the secondcommunication mode receiver is originated by a universal terrestrialradio access (UTRA)-TDD cell.
 18. The IC of claim 16 wherein the secondtype of signal received by the second communication mode receiver isoriginated by a global system for mobile communications (GSM) cell. 19.A multi-mode wireless transmit/receive unit (WTRU) comprising: (a) atleast one antenna configured to receive and transmit at least twodifferent types of signals; (b) a first communication mode receiverconfigured to receive a first type of signal from the antenna; (c) asecond communication mode receiver configured to receive a second typeof signal from the antenna; (d) a first communication mode transmitterconfigured to generate and send the first type of signal to the antenna,wherein the first and second communication mode receivers simultaneouslyreceive signals from the antenna, and the first transmitter sends thefirst type of signal to the antenna while, at the same time, the secondreceiver receives the second type of signal from the antenna; (e) amodem electrically coupled to the second communication mode receiver;(f) an interference canceler control circuit electrically coupled to themodem; and (g) a vector multiplier electrically coupled to theinterference canceler control circuit, wherein the interference cancelercontrol circuit receives measurements of noise measured by the secondcommunication mode receiver via the modem, and adjusts the phase andamplitude of the vector multiplier to minimize the noise.
 20. The WTRUof claim 19 further comprising: (h) a triplexer electrically coupled tothe first communication mode receiver; (i) a transmit/receive switchelectrically coupled to the antenna and the triplexer; (j) a firstcoupler electrically coupled to the triplexer and the firstcommunication mode transmitter; (k) a second coupler electricallycoupled to the vector multiplier, the triplexer and the secondcommunication mode receiver; and (l) a bandpass filter electricallycoupled to the first coupler and the vector multiplier.